1. Field of the Invention
The present invention generally relates to fiber optics and, more particularly, to a cladding configuration for increasing the efficiency of a multiclad optical fiber.
2. Background Art
There is a demand for fiber optics of increased output power. Amongst the solutions for obtaining fiber optics of increased output power, the input pump power (for example, a pump from a laser diode) can be increased. However, the coupling of the input power into the optical fiber is subjected to losses of light as the pump width typically increases with the output power, and coupling efficiencies then limit the upgrading of the power input. Pumping also increases in cost with lower coupling efficiencies.
Another solution to increasing the output power of an optical fiber system is to increase the coupling efficiency between the input power and the optical fiber. The pump source is positioned at an input end of an optical fiber. The diameter of the optical fiber is a limitation to the coupling efficiency. Hence, various configurations have been provided to overcome this limitation and thereby increase the input pump power in optical fibers. U.S. Pat. No. 5,268,978, issued to Po et al. on Dec. 7, 1993, discloses an optical fiber laser and geometric coupler. More precisely, the coupling efficiency between a light source and an output optical fiber is increased by providing coupling means and a cylindrical lens therebetween. The coupling means include a plurality of input optical fibers having respective input ends, each associated with a light-emitting facet of the light source. Each of these input optical fibers has an output end. A cylindrical lens is positioned between the output ends of the plurality of input optical fibers and the output optical fiber to focus light emerging from the facets onto the input end of the output optical fiber.
It is also known to increase the coupling surface between the power input and the optical fiber. For instance, U.S. Pat. No. 4,815,079, issued to Snitzer et al. on Mar. 21, 1989, describes a fiber-optic arrangement wherein a side-pumping input fiber is coupled longitudinally to an optical fiber so as to increase the coupling surface between the power input and the optical fiber. This is generally illustrated in FIG. 1 of the prior art, wherein the optical fiber is shown at 10 and the side-pumping input fiber is shown at 11. The side-pumping fiber 11 is the pump source for the optical fiber 10. The optical fiber 10 has a doped core 12, a first cladding 13, and a second cladding 14. The second cladding 14 defines the outer periphery of the optical fiber 10. A portion of the second cladding 14 is removed so as to expose the first cladding 13 of the optical fiber 10. The side-pumping input fiber 11 has a core 15 and a first cladding 16. A portion of the first cladding 16 of the side-pumping input fiber 11 is removed such that the first cladding 15 is exposed. Accordingly, the optical fiber 10 and the side-pumping input fiber 11 are interconnected by the exposed portions of the first cladding 13 of the optical fiber 10 and the core 15 of the side-pumping input fiber 11 being coplanar. An affixing material (not visible) may bond the optical fiber 10 to the side-pumping input fiber 11. The indexes of refraction are such that light from the side-pumping input fiber 11 is coupled into the optical fiber 10 to potentially be absorbed by the doped core 12. The interface surface between the pump source (i.e., the fiber 11) and the optical fiber 10 can thus be adjusted, so as to maximize the amount of the light from the pump source reaching the optical fiber 10, and thus improving the coupling efficiency therebetween.
Although the coupling efficiency between pump source and optical fiber has improved as a result of novel configurations such as the ones described above, other configurations providing further coupling efficiency improvements and doped core absorption efficiency are desirable particularly for taking advantage of still higher power pump sources.